The present invention relates generally to systems for controlling exhaust emissions produced by an internal combustion engine, and more specifically to such systems including an auxiliary emission control device for accommodating control of condensation effects resulting from cooled EGR.
When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). This problem is aggravated through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.
One known technique for reducing unwanted emissions such as NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold valve, for controllably introducing exhaust gas to the intake manifold. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.
While EGR systems of the foregoing type are generally effective in reducing unwanted emissions resulting from the combustion process, a penalty may be paid for the use of EGR in the form of potentially damaging engine operating conditions. For example, when employing cooled EGR, exhaust containing condensation in the form of sulfuric acid and other components may collect at the EGR cooler outlet and in the air intake system of the engine. Excessive condensation may accordingly lead to engine corrosion and damage. A tradeoff thus exists in typical engine control strategies between acceptable levels of NOx production and safe (e.g., non-damaging) engine operating conditions, and difficulties associated with managing this tradeoff have been greatly exacerbated by the increasingly stringent requirements of government-mandated emission standards.
Historically, the Environmental Protection Agency (EPA) has promulgated limits for allowable levels of certain exhaust emissions such oxides of nitrogen (NOx). Recently, the EPA has recognized that mandated exhaust emission limits should allow engine behavior that deviates from expected engine operation under certain conditions, such as in order to avoid damaging or potentially damaging engine operating conditions. Deviation from expected engine operation, in this context, is generally allowable through the use of one or more so-called auxiliary emission control devices or AECDs. For purposes of the present invention an AECD is defined as a software structure that controls, as a function of one or more engine operating parameters, a current operational state of the engine.
The present invention is directed to a condensation protection AECD operable to control exhaust emissions in a manner that protects the engine from the formation of excessive condensation in an EGR cooler outlet and air intake system which may lead to formation therein of sulfuric acid and/or other corrosive compounds.
The present invention is further directed to such an AECD operable to estimate damage to each of the EGR cooler outlet and air intake structures resulting from allowed condensation conditions.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.